I usually know someone who needs a phone. I generally gift my old phone to someone when I buy a new one.
If I use power at 7:00PM where I live, it is likely to be wind generated. If I use it at 3:00PM, a good part of it is likely to be from a gas turbine. It's better to use power when the demand is low.
I think of it as education. I try not to use the AC, wash dishes, clothes or whatever when demand is high. Every little bit helps.
If you use power that generates one kg of CO2, but you do things that reduce the production of CO2 by two kg, you have effectively used negative one kg. Because of your actions, there is one less kilogram of CO2 in the air.